This invention relates to refrigeration compressor units especially but not exclusively units for small refrigeration units such are suitable for use in domestic ice cream makers, small refrigerators and similar appliances. Such units must be compact, quiet, reliable and economical to manufacture and operate
Compressor units for domestic refrigerators are commonly of the sealed unit type in which both the compressor and a motor permanently coupled to the compressor are located within an enclosure which is completely and permanently sealed except for refrigerant connections to the remainder of the refrigeration unit. Such a unit has the disadvantages that failure of either the motor or the compressor requires both to be discarded, different sealed units are required for electrical supplies requiring different motors, even though the compressor is identical, and two devices, both of which generate unwanted heat. are thermally coupled within the same enclosure.
It is known in compressor units for automotive air conditioning systems, which are engine driven, and thus require a clutch mechanism, to utilize an electromagnetic clutch between a belt driven pulley and the compressor.
it is also known to use magnetic couplings in drives for pumps so as to avoid the necessity of sealing a drive shaft entering the pump chamber. Examples of such arrangements are to be found in U.S. Pat. No. 3,584,975 (Frohbieter); U.S. Pat. No. 3,680,984 (Young et al.); U.S. Pat. No. 4,065,234 (Yoshiyuki et al.); and U.S. Pat. No. 5,334,004 (Lefevre et al), and in ISOCHEM (Trademark) pumps from Pulsafeeder. Although the first of the patents relates to a circulation pump for an absorption type air conditioning system, the use of a permanent magnet coupling in the drive to the compressor of a compressor type refrigeration unit has not to the best of my knowledge previously been proposed.
Reasons may include the sharply fluctuating torque required by piston type compressors normally used in such systems.
In the interests of smoother and more silent compression, there has been some adoption of scroll type compressors in compression type refrigeration units, available for example from Lennox, Copeland and EDPAC International.
An alternative form of piston compressor which has been proposed, although not to the best of my knowledge for refrigeration applications, is the rotary piston compressor using a lobed rotor in a trochoidal chamber and having some superficial resemblance to rotary piston engines such as the Wankel engine although the operating cycle is substantially different and the shaft is driven by an external power source rather than being driven by the rotary piston. Such compressors are exemplified in U.S. Pat. No. 3,656,875 (Luck); U.S. Pat. No. 4,018,548 (Berkowitz); and U.S. Pat. No. 4,487,561 (Eiermann).
U.S. Pat. No 5,310,325 (Gulyash) discloses a rotary engine using a symmetrical lobed piston moving in a trochoidal chamber on an eccentric mounted on a rotary shaft and driven through a ring gear by a similarly eccentric planet gear rotated at the same rate as the eccentric, the gear ratio of the ring gear to the planet gear being equal to the number of lobes on the rotor, typically three. The apices of the lobes trace trochoidal paths tangent to the trochoidal chamber wall thus simplifying sealing. There is no suggestion that similar principles of construction could be used in a compressor.
In its broadest aspect, the invention provides a compressor for a refrigeration unit having a stator, a rotor orbiting in engagement with the stator to cyclically open, fill with refrigerant gas from at least one inlet port, compress and discharge compressed refrigerant gas through at least one discharge port, a rotary drive for orbiting the rotor, a driven element of a magnetic coupling in driving connection with the rotary drive, a casing sealed save for the ports and enclosing all of the foregoing components, a driving element of the magnetic coupling outside of the casing in close proximity to the driven element, and means to rotate the driving element.
Preferably the rotor is a multilobed rotor orbiting within a trochoidal chamber defined by the stator, although a scroll type compressor with stationary and orbiting scrolls may also be utilized. Most preferably, a three lobed rotor is journalled on an eccentric carried by a shaft of the rotary drive and has a ring gear driven by a gear of the rotary drive having the same eccentricity as the eccentric and rotated in synchronism therewith, the gear ratio of the ring gear to the eccentric being three to one.
Further features of the invention will be apparent from the following description of a presently preferred embodiment thereof.